The invention relates to an electric machine, in particular a three-phase generator for motor vehicles and a method for producing a machine of this nature.
An electric machine of this nature is made known in DE 199 39 808 A1. According to said publication, the permanent magnets in the open spaces between the intermeshing claw-pole fingers are inserted into a retaining ring that absorbs the centrifugal forces acting on the permanent magnets produced when the machine operates. The retaining ring is welded together with the adjacent claw-pole fingers on both sides of its axial sections.
Using a xe2x80x9cwindingless rotorxe2x80x9d as an example, a means of attaining the object of the invention described hereinabove has the advantage that welding the retaining ring results in a permanent connection being formed between the free claw pole conductive element and the claw pole plate situated on the rotor shaft, allowing the connection ring used heretofore to be eliminated. Since, in the case of xe2x80x9cslip-ring rotorsxe2x80x9d, both claw poles are usually mounted on the rotor shaft, a fixed connection is not required there.
Rather, it has the disadvantage that a special working step performed at an additional processing station is required to make the welded connections between the retaining ring and claw-pole fingers.
The goal of the present means of attaining the object of the invention is to permit the simplest possible installation of the retaining ring between the claw-pole fingers.
Compared to the prior art, the electric machine according to the invention having the characterizing features of claim 1 has the advantage that the reconfiguration of the claw-pole fingers enables the creation of nothing more than a positive connection between the permanent magnets and the retaining ring, instead of a fixed connection. As such, the costly need to produce welded connections is eliminated, and the centrifugal forces acting on the retaining ring are still reliably absorbed by the claw poles.
A further advantage is the fact that, due to the zigzag configuration of the retaining ring, the holders for the permanent magnets no longer extend into the winding space for the excitation winding, which means that an excitation winding having a larger cross-section and, therefore, greater excitation power can now be housed in the claw-pole rotor.
Compared to the prior art, the method according to the invention for producing an electric machine according to the characterizing features of claim 6 has the advantage that the retaining ring and permanent magnets can be installed fully automatically between the claw poles of the rotor on the existing assembly line for producing a claw-pole rotor without permanent magnets at an additional assembly station inserted there.
As an additional means for restricting the elastic pressing-upward of the claw-pole fingers by the centrifugal forces within narrow limits, the longitudinal slits on the lateral flanks of the claw-pole fingers are interconnected via an end-face slit on the tip of the claw-pole fingers, into which said end-face slit a bead integrally molded on the connection section of the retaining ring engages. Furthermore, to increase the bending stiffness of the axial sections of the retaining ring, it is advantageous to equip each of them with a radially outwardly directed longitudinal hollow. Simple production of the retaining ring can be attained by punching and stamping the retaining ring out of a piece of non-magnetic sheet metal. In the simplest manner possible, a punched-out sheet metal strip is used that is bent and stamped in the shape of an open retaining ring.
Although the inventive features can be used particularly advantageously with collector rings, they can also be realized on xe2x80x9cwindingless rotorsxe2x80x9d, provided that the fixed claw-pole connection is created there using additional means or measures. In that case, the conductive element forms one of the two claw poles.
In the production of the electric machine according to the invention, axial longitudinal slits for accommodating the axial sections of the retaining ring are recessed in the lateral flanks of the claw-pole fingers in a process step in preparation for assembly of the retaining ring. At an additional assembly station, the retaining ring with a zigzag configuration is first inserted into the longitudinal slits in the claw-pole fingers of the first claw pole by means of one longitudinal side of its axial sections. To accomplish this, the first claw pole is mounted on a tool holder that has a magnetic ring enclosing the claw-pole fingers and the retaining ring from the outside, which said magnetic ring is partially magnetized in the region of the axial sections of the retaining ring. To install the permanent magnets, they are advantageously first inserted in an annular arrangement in axial holes of a round magazine. The round magazine is then positioned over the exposed, end-face connection section of the retaining ring in such a manner that the axial holes with the permanent magnets come to rest in pairs between the connection sections of the retaining ring. Using an annular plunger having fingers matched with the holes in the round magazine that is located above the round magazine, the permanent magnets are pushed axially out of the holes into the space between the claw-pole fingers until the permanent magnets rest against each of the lateral flanks of a claw-pole finger. As they are pushed further, the permanent magnets glide along the side of the lateral flanks of the claw-pole fingers, thereby assuming an inclined position, where they are held by the magnetic ring by means of its partial magnetization. After the plunger and the round magazine are removed, the permanent magnets are set into their final position on the axial sections of the retaining ring by means of a shaped plunger having a claw pole-shaped contour plunging axially into the magnetic ring of the tool holder, where they are held by the magnetic ring. The first subassembly which is preassembled in this fashion is joined, together with the tool holder and the magnetic ring, with the rotor shaft, the pole core, the excitation winding, and the second claw-pole, and the first claw-pole is placed on the rotor shaft with an interference fit. The second claw-pole is placed on the rotor shaft with a sliding fit, then positioned by the first claw-pole and the retaining ring, and, finally, caulked with the rotor shaft.